put my pre-amp together and now the left channel is playing distorted :( - Page 2 - diyAudio
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Old 2nd April 2003, 07:37 AM   #11
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One question: Are both channels as loud as the other one ?

Regards

Charles
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Old 2nd April 2003, 07:53 AM   #12
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Quote:
Originally posted by elizard
well i think i'll hit the sack now .. too tired to even see straight, gonna keep on working on it tomorrow though.
A little while ago, I was having a problem with a breadboarded circuit which was misbehaving. (I have no scope at home, just a DMM) Frustrated, I left it alone and went to bed. While lying in bed, I kept thinking about it, but no solution. While sleeping, I had a dream in which I was taking a lab exam at school. In the dream I did everything right. I used all the right components, configured them with the correct polarities, and decoupled the op-amps. For some reason or another, the decoupling thing stood out to me. When I woke up, I re-checked the circuit and realized I forgot to decouple one of the op-amps! Thank you subconscious! The other parts of my dream was about girls, but I don't think I'll ever really figure them out.

Morals of the Story:
1) Sometimes it's best to stand back from a problem to clear your head, and then re-tackle it.
2) Girls don't make sense.
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Old 2nd April 2003, 09:25 AM   #13
Cobra2 is offline Cobra2  Norway
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Quote:
2) Girls don't make sense.
sorry, could not resist...

(The 2 things God created, that cannot be tamed...;
girls and cats).

Arne K
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Old 2nd April 2003, 12:48 PM   #14
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elizard,

Check the caps polarity (if they are electolythics) around that op-amp.
Or maby a defective cap.
Normally on the supply/bypass caps near the op-amp.
Or some mistake while you were soldering.
Check under the circuit, near that op-amp, if you didn't join supply and signal tracks/components while soldering.
Do it slowly, take your time, see everything.
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Old 2nd April 2003, 09:21 PM   #15
elizard is offline elizard  Canada
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well .. i've narrowed the problem down a little bit
first i measured resistance across R26 - and its next to nothing, althought it should be 1.05k

So i pulled R26 out, and it measures 1.05k no problem.
i put it back in ..

i pulled J13, measured resistance across R26, gets 1.05k ok
so then i soldered J13 back in, and measured resistance from the opposite leg of R26 and on a few spots, and it only gets resistance from the last couple resistors (R31 i think? for phones output btw ..)

so i'm thinking its a short somewhere
could it still be that a component is not working (i.e. resistor/diode/transistor is dead?) or is it almost definitely a short while soldering?
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Old 3rd April 2003, 05:43 AM   #16
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Hi elizard

You definitely (though unintentionally) seem to be loading the output of the opamp too hard.

The low resistance across R26: Was it measured with anything connected to any output (phones, preamp .... ) ? If yes how does it measure with nothing connected to any output ?

If there is nothing connected to any output and you don't have any solder bridges (and still the low resistance) then a component might be defective (i.e. cause a short to ground). Some suitable candidates: C5, C7, the output sockets ...... Is L1 wound with bare wire that might touch the ground somehow ?

Regards

Charles
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Old 3rd April 2003, 06:18 AM   #17
Netlist is offline Netlist  Belgium
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Quote:
Originally posted by elizard
well .. i've narrowed the problem down a little bit

Can't find J13. Do you mean SK13? Pin13 of SK7?
If you measure "next to nothing", it's probably not a bad component. But what is next to nothing?
BTW, 1K5 is 1.5k and not 1.05k.
Check connector SK7. Those pins are close together and I know from experience that soldering connectors like that easily give solder bridges. They can be very tricky. IC-sockets have the same problem. Those are the first places to look. Use a magnifier glass, if necessary.
What do you get at both side of R8 with respect to ground? (Amp in off position, no in or outputs connected.)

/Hugo
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Old 3rd April 2003, 08:36 PM   #18
elizard is offline elizard  Canada
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Well, I fixed it!!!

Even thought I still don't know what hte problem is, i managed to fix it .. a little unorthodox
I managed to narrow the problem down to a signal from the left channel that's going towards the headphones jack is touching ground somewhere ..

The place I narrowed it down to was between J19 and L1. There is a direct connection between the two spots (if you look at the board layout in the manual, you'll see J19).
I disconnected J19, and L1, then measured between one point of where J19 was supposed to be connected and the ground - there's a connection (0ohm readout). I measured between one point of L1 (the point that's further away from the front of the board) and the readout was 0ohm as well ..
So somewhere between J19 and L1 there's contact w/ the ground.
I ran a piece of wire soldered to one end of J19 and to one leg of L1, measured between the left channel out and ground, 1.04kohm .. good!

Powered it up, no distortion on either channel.

So, total so far is 6 hours of putting the board together, and 4 hours of troubleshooting this little problem. Not too bad for my first soldering experience since grade 9 electronics class (5 years ago).

I'm perfectly satisfied w/ the preamp btw ..

Thank you for all the help .. I'll be sure to ask for more when I order the amps (btw. i'm ordering a set of K8040's as the amps)

PS. I couldn't see any solder bridges, and there was still the problem even after I removed ALL the solder from the problematic contact points.
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Old 4th April 2003, 06:02 AM   #19
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Quote:
Originally posted by elizard
Well, I fixed it!!!

Even thought I still don't know what the problem is, I managed to fix it .. a little unorthodox.

So, total so far is 6 hours of putting the board together, and 4 hours of troubleshooting this little problem. Not too bad for my first soldering experience since grade 9 electronics class (5 years ago).
Well... Congratulations!!!

I'd say you did pretty well considering your only experience was in grade 9. Let me guess... your project back then was two LEDs alternately blinking on and off?

Even though it probably was probably a big pain in the a**, you should appreciate the fact that you did have a problem. I think you probably benefitted the most (knowledge and experience-wise) from identifying and solving your problem. And even though we offered a few suggestions, It seems as though you fixed it by yourself. Pat on the back!

As for you not figuring out the exact problem, well, sometimes things turn out like that. I once volunteered to fix my friend's microwave. They aren't that complicated, so I figured there would be an obvious problem. I prodded around looking for a pitch black bad-smelling resistor, or something of the like. After poking around a while, and having limited test equipment on hand(only a crappy DMM), I decided to call it quits. I put it back together and what do you know... worked perfectly. To this day, I know not what I did.

Anyways, I'm glad it all worked out for you. Good work. Now go tackle those amps.

I just thought I'd give the usual you-can-die disclaimer with regards to repairing microwaves. I am edumucated(as Homer would say). Don't try it at home. or school. or work. or in the park. or at the beach. yeah. time to stop writing...
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Old 4th April 2003, 06:14 AM   #20
elizard is offline elizard  Canada
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lol@seangoesbunk!

yeah .. i do appreciate encountering the problem

to tell you the truth, after i put the whole thing together i was a little dissapointed because there wasn't much in terms of a challenge ..
all it was is just slap the components on, solder, slap more on, solder more ..

but then i had to sit there for 2x2hours wondering what's wrong, desolder, resolder, check .. check continuity, plug in .. all that and more
and it was fun .. all i can say!

and now i'm reaping the benefits ..
since i don't have an amp that has a pre-amp in, i have to listen through the headphones (which is just fine for me!) .. and WHOA!

i'm also using the phono in on the pre-amp as well .. turned off the phono preamp on my cheapo turntable

put on blow by blow by jeff beck .. side 2 ..
just beautiful!
without any burn in for the preamp .. so far i've managed to hear more stuff that i've never heard before on 1/2 the volume w/ +6db than i've managed to hear on 80% the volume on my receiver .. amazing!
and VERY clean .. very little hiss/hum on phono in (due to my crappy receiver i assume .. i'll have to solder a pair of decent interconnects to it) .. NO hiss/hum on the cdplayer even on the highest volume .. truly amazing!
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